Here’s what’s going on. For Windows on X86, Microsoft is giving
other browsers basically the same privileges it gives IE. It’s not
great that you don’t get those privileges (certain API access)
unless you’re the default browser and I think that’s deeply unfair
(a post for later,) but at least we’re able to build a competitive
browser and ship it to Windows users on x86 chips.

But on ARM chips, Microsoft gives IE access special APIs
absolutely necessary for building a modern browser that it won’t
give to other browsers so there’s no way another browser can
possibly compete with IE in terms of features or performance.

In other words, Microsoft is setting policies for Windows for ARM that are a lot like Apple’s policies for iOS. These policies and restrictions make just as much sense for Microsoft as they do for Apple. The problem for Microsoft, as Dotzler points out in the comments on his piece, is that Microsoft has made antitrust agreements that seemingly preclude such restrictions.

Serious question: What if Windows 8 for ARM, instead of being called “Windows RT”, were instead called, say, “Metro OS”? Would that make a difference? Is Dotzler arguing that Microsoft should not be permitted to ship a version of Windows that locks out third-party browsers, or that Microsoft should not be permitted to ship any OS that locks out third-party browsers?